1. Field of Invention
This invention relates to methods of preventing acoustical resonance in pipes of any length and specifically those pipes that conduct sound waves between a noise source and another part of a closed system or into the atmosphere.
2. Discussion of Prior Art
The theoretical problem of sound wave suppression in pipes was partially solved by Herschel using the means of sound wave interference in 1833 (Phil. Mag. Vol. 3, page 111, 1833). This theoretical approach by Herschel was put into practical form by Quincke in 1866 (Ann. d. Physik. Vol. 28, p. 177, 1866). In 1928 Stewart showed that the simple Herschel explanation was incomplete and needed to take into account additional reflections (Pys. Rev., Vol. 31, page 696 1928). Stewart showed that sound wave interference pipes not only suppressed the fundamental and harmonics by the use of interfering pipes but many other frequencies as well.
Wave interference type mufflers are disclosed in U.S. Pat. No. 3,580,357 issued May 25, 1971 to Whitney, Pat. Nos. 3,700,069 issued Oct. 24, 1972 to Rausch et al. Pat. Nos. 3,948,348 and 3,948,349 issued Apr. 6, 1976 to Bychinsky, Pat. No. 3,913,703 issued Oct. 21, 1975 to Parker and Pat. No. 4,165,798 issued Aug. 28, 1979 to Martinez.
Such arrangements have two relatively open exhaust flow paths through which a total exhaust stream is divided. In these arrangements the acoustical lengths of the concentric or other pipes are selected to be 180 degrees out of phase at their termination, to cancel the unwanted frequency. In addition, the Rausch patent adds a leakage path to suppress high frequencies.
The problem with approach used in the above patents is that all of them fail to take into account the fact that mufflers in general are connected to exhaust and or tail pipes. These pipes resonate at some fundamental frequency as well as various harmonic frequencies associated with the length of the pipe. All internal combustion engines and most fans and pumps emit a broad band of sound frequencies. Thus they will acoustically excite the pipes attached to them. Suppression of one or a few frequencies will still allow other frequencies to pass through the pipes, leading to unwanted noise.
It is important to note that most practical mufflers are designed to suppress the fundamental frequencies of the pipes to which they are connected.
Two examples of noise from unsuppressed pipe resonance are race car exhausts and large leaf blowers.
With my intention the pipes will not resonate, and the need for the complex soundwave traps are proposed by the above patents are no longer needed. The above patents have failed to attack the basic problem. They have failed to see the forest for the trees.
In current automotive mufflers in practice, high frequencies are suppressed by xe2x80x9cbean cansxe2x80x9d. These are discreet chambers concentric to the exhaust flow pipes. Louvers in the exhaust flow pipe connect acoustically with the chambers. To suppress the low frequencies associated with exhaust and tailpipe resonance, large tuned chambers are used (often with Helmholtz resonators).
Each of the above cited patents tend to attenuate a discrete frequency or frequencies by the principle of sound wave interference. The frequencies that these mufflers tend to attenuate are usually those multiple frequencies that are generated by the engine, rather than the most important cause of low frequency noise, that created by the resonant pipes by means of which these mufflers are connected into the system.
Accordingly, the main object of my invention is to eliminate or greatly reduce acoustical resonance in pipes of any length by means of sound wave interference.
A further object of my invention is to greatly reduce the noise produced by non-muffled exhaust or intake pipes in fluid flow systems. This includes gas or liquid systems. Yet another object of my invention is to eliminate or greatly reduce the size of mufflers or intake silencers in fluid flow systems.
Yet another object of my invention is to eliminate destructive resonance in hydraulic system pipes.
yet another object of my invention is to produce an acoustically non-resonant pipe that is easy to manufacture.
Yet another object of my invention, in the case of leaf blowers and similar machines, is to impart a rotary motion to the gas flow to provide increased stability of the jet which is issued from the pipe.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description thereof.